inbreeding depression- caused by reduction in the frequency of heterozygous genotypes.

Small populations and brief bottlenecks

Small population : Populations of a finite size in which mating between related individuals are likely to occur.Brief Bottleneck : Temporary reduction of population to very small number of individuals.

Why is is hard to distinct large and small population?relationship between population size and accumulation of homozygosity due to mating between relatives is continuos.

Factor that accumulate homozygosity-inbreeding

The smaller the number of individuals, the greater the likelihood that mating between related individuals will affect mean fitness.

inbreeding effective population size:population size of an ideal, randomly mating population that would accumulate homozygosity at the same rate as the population of interest

Results & Discussion

purging is the expression ofbottleneck' effect.

severe bottleneck' effect led to fixation of deleterious alleles.

multiple severe bottlenecks-large effect on population viability, suggesting the accumulation of relatedness resulting from bottlenecks might have a threshold effect on population viability.

no significant effect of fouder relatedness on population size- pop founded with siblings < founded with nob siblings

unable of founders to establish its population is due to history of bottleneck

purging hypothesis predict difference between growth of pop founded with siblings and non siblings decrease the number of past bottleneck

purging is expected to take place within thefirst few generation of intense inbreeding

the use of. inbreeding as management tool may increase extinction risk

Conclusions

(Crnokrak & Barrett, 2012) Purging is important evolutionary force in small population.

Purging effect can be avoided by:

a)traditional approach by minimizing the severity and duration of population bottleneck.

b) use captive breeding design that prevent mating among relative.

There is lack of purging in Gambusia population due to

High deleterious alleles or over-dominance contributes to inbreeding depression

Insufficiently stressful selective environment

Drift overwhelming selection

Methods

null hypothesis: No difference in population growth among bottleneck history treatments based on relatedness of founding individuals

virgin offspring

omit individuals with large morphological deformities

usage of 12 populations

6 population experienced a bottleneck of a single pair of individuals

6 population of offspring of fish maintained in a large out-bred stock that had experienced no bottleneck

serial bottleneck treatment

2 population will be used

split to 12 mesocosms for 12 treatments

10 extict

Usage of Mesocsms

Advantage

Fishes are exposed to be more complex environment than organisms in lab studies

offers an opportunity to examine responses of vertebrate population under similar conditions